Marans Genetics Question

If both parent birds are Black Copper Marans (perhaps not SOP, but standard coloring, body shape, etc) and they have a very blue looking offspring, what genetics are in play there? I know there has to be blue in one parent, but if is blue recessive like eye color, wouldn't it have to be more predominate in both parents?

That calls for speculation. If it is the Blue from B/B/S, one of the parents would have to be Blue or Splash. The B/B/S gene is a partially dominant gene, it’s kind of weird. If both genes at that gene pair are B/B/S, you get Splash. If only one is B/B/S you get Blue. If none are B/B/S, you default to Black. But that only affects feathers or parts of feathers that would have originally have been black, it does not affect other colors like red, buff, or white.

Another possibility is that it is not Blue but instead is Lavender. Lavender is a recessive gene that behaves like you would expect a recessive gene to behave, none of this partially dominant stuff. It is also a modifier of black, it does not affect other colors.

With chicken color and pattern genetics there are always exceptions and other possibilities. There are a lot of modifiers that I don’t come close to understanding how they work. But from what I know the logical conclusion is that both parents have Lavender if neither is showing Blue or Splash.

Okay, after doing a bunch of research, he is not blue. Although he was definitely hatched bluish colored, he is predominately black with a huge amount of blue hue to his feathers. Parents from Texas:
And the only pic i have of him (can't really see the hue)
I know he's not a pretty bird (10 weeks old) and will probably just end up having a share in my layer flock protection. I just thoughthe was so different from his siblings - what was up with his genetics?
Here's a typical sibling; the one at the feeder, not the OEs.
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Blue/black seems to be what is co-dominant, or additive, which is actually very cool. Its like blood type in humans.

Is the blue kind of iridescent? I have seen that in other bird species and I believe it is from structural formations rather than pigmentation, which the black, blue, splash spectrum seems to be. The iridescence is us seeing only the limits of the vision the birds can see (https://www.backyardchickens.com/a/information-on-chicken-eyesight), so he may be very pretty to your chickens, but we just can't see it.